In general, Gigabit Passive Optical Network (GPON) technology standardized by the ITU-T G.984 group is one type of Fiber to the Home (FTTH) technology for efficiently providing transmission bands to subscribers and servicing a variety of protocols. In the GPON technology, one optical line terminal (OLT) is connected to a plurality of optical network terminals (ONTs) in a point-to-multipoint structure, as in Ethernet-PON (EPON) technology. Current GPON technology has a symmetrical or asymmetrical structure capable of providing a downstream transmission band of 2.488 Gbps and an upstream transmission band of 1.244 Gbps, unlike the EPON technology capable of providing only upstream/downstream transmission bands of 1 Gbps.
FIG. 1 illustrates a structure of a GPON ONT according to a standard of the ITU-T G.984 group. In the GPON ONT according to the G.984 GPON standard, a GPON protocol layer is present under a data link layer and converts a variety of services (e.g., ATM, Ethernet, and TDM) of the link layer into a GPON frame and transmits the GPON frame. In the GPON ONT, a GPON protocol consists of a physical layer B100 and a transmission convergence (TC) layer B101. The physical layer B100 performs photoelectric conversion, burst transmission, clock extraction, and the like. A current G.984 standard allows for downstream data rates of 1.244 Gbps and 2.488 Gbps and upstream data rates of 155.52 Mbps, 622.08 Mbps, 1.244 Gbps and 2.488 Gbps. However, low-rate transmission bands of 155.52 Mbps and 622.08 Mbps are not actually used. The TC layer B101 includes a GTC framing sub-layer 100 and a GPON encapsulation method (GEM) TC adaptation sub-layer 101.
The GTC framing sub-layer 100 performs multiplexing or demultiplexing into a GPON transmission convergence (GPON TC, GTC) frame using frames and physical layer operation administration maintenance (PLOAM) message information 104 received from a GEM client 106, DBA information 102, and synchronization information. The TC adaptation sub-layer 101 performs connection or disconnection to or from an upper service using a GEM Port-ID identifier with respect to GEM service. The GEM client connects to services such as Ethernet and TDM. An upstream bandwidth control (UBC) transmission layer 102 extracts a transmission band time assigned by the GPON OLT to control an upstream transmission time for ONUs. The physical layer OAM (PLOAM) 104 delivers information for management of the GPON physical layer and the framing sub-layer. The ONT management control interface (OMCI) 103 manages statistical information and state for the GPON ONTs.
The GPON ONT defined in the G.984 standard cannot efficiently provide high-definition IPTV service with hundreds of channels to subscribers due to its limited transmission band. Accordingly, there is a need for a scheme for providing high-definition IPTV service with hundreds of channels to subscribers.